Warning where the Big One will hit

By Wallace RavvenThursday 8 December 2011

UC Berkeley is partnering with two other universities, a philanthropic
foundation and industry to conduct earthquake research that could lead to a
warning system. People could then have
time to dive for cover, and transportation and utility systems could shut down operations.

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A major fault ruptures somewhere along the 70-mile-long Hayward
Fault. But where? Is the break at just
one point along the restless slab, or many?

Answers are crucial to predicting where the worst shock will
hit and how much damage it will cause. The underground details can provide a
precious five- to 30-second warning between the time a temblor is detected and when
its destructive energy reaches the surface.

But seismology cannot yet supply the data. Scientists don’t adequately understand the
basic physics of the fault-rupturing that triggers the largest quakes — magnitude 7 or greater. And without that insight, they can’t warn citizens, utilities
and industry where or what destruction is on its way.

An unusual alliance between a philanthropic foundation, universities
and industry has launched a three-year research effort to advance this
knowledge and develop a prototype seismic and GPS-based network to pinpoint
sites of rupture within seconds.

“I am confident that this research will allow us to develop
a truly effective prototype,” says Richard Allen, director of the UC Berkeley Seismological
Laboratory. “With that demonstration, we would seek federal funding for a
full-scale West Coast early warning seismic network.

“This would be tremendous progress, and could provide in
some cases as much as 30 seconds of advance warning to cities, businesses — to millions of people.”

Allen stresses that the goal is not predicting quakes
themselves, but rather the location and likely extent of damage of quakes
within a few seconds after the deep-earth rupture.

Caltech and University of Washington seismologists join
Berkeley in the research project.

Google.org and Deutsche Telekom's Silicon Valley Innovation
Center are providing financial support for developing the prototype. They also will be at the receiving end of early warnings in the “practice” phase of the
project. The companies hope that if fully implemented, the system could reduce
damage to commercial operations when a major quake hits.

Developing a quicker, more accurate warning system can alert
individuals to dive for cover, give transportation systems and utilities time
to shut down operations and allow delicate procedures — from surgery to precision
manufacturing —
to be halted before a destructive quake arrives.

“Our goal is faster estimation of the precise location and
likely degree of damage,” Allen says. “We need to limit destruction, but also
limit false alarms so communities and businesses are spared costly emergency
precautions.

“If we can predict that the real damage from a rupture along
the Hayward Fault won’t hit, say, San Jose, but instead will severely jolt a
city 20 miles farther north along the fault, that could save resources and
lives.”

Faults are fractures in slabs of rock beneath the surface, sometimes
as deep as 10 miles down. When stress builds up between rock on opposite sides
of a fault, a rupture can occur, releasing a tremendous amount of energy. The rupture can be small or large, and it can
be isolated or can trigger a rapid series of subsequent ruptures, Allen
explained.

Whether a rupture will trigger other slippage farther along the
fault influences tremendously the location and extent of surface damage.

Researchers already know the typical pattern of energy
released by quakes. Seismographs first
detect a burst of energy, known as the P-wave, as it heads toward the surface.
P-waves carry relatively little energy and rarely cause damage. They are followed by the so-called S-waves,
which reach the surface about two seconds later and carry the slipped fault’s true destructive force.

Quakes of magnitude 6.5 or less usually arise from a rupture
in only one location along a fault — its epicenter. Seismologists can
confidently predict that damage will occur in regions closest to the epicenter.

But in quakes of 7.0 or larger — “the big ones” — the rock
slabs on opposite sides of a fault can slip and slide in a number of regions.
In this case, surface damage is more dependent on the distance from the fault
than proximity to the first slip, the epicenter.

“We need to track the fault rupture as it happens and update
our warnings as necessary,” Allen stresses.

The new project’s basic research is two-fold: to refine
current understanding of how rupture patterns affect the location and amount of
damage, and to use this understanding to predict location of major damage
seconds or tens of seconds before they occur.

Active faults are often five to 10 miles below the surface –
beyond the reach of any imaging technology, Allen explained. Unable to see the different
sites and types of movement, researchers will primarily focus on refining
computer models to more accurately reflect the key physical triggers and
constraints at play along a deep-seated rupturing fault.

The trick will be to “synch” detailed records of past quake
damage with the models of fault dynamics. Then seismology will reach the goal
of predicting the trajectory of the world’s worst earthquakes.

Photo at top of page: The control room at the Japanese Meterological Agencywith its earthquake early warning system. Photo by Richard Allen